DESCRIPTION:(Adapted from the Investigator's Abstract): Epidemiologic, immunologic and clinical studies indict Porphyromonas gingivalis as an important pathogen in periodontitis. In contrast to many pathogens, P. gingivalis isolates infrequently display genotypic clonality. As many as 100 different clonal types have been found among periodontitis patients. This proposal will explore the possibility that repeated DNA sequences, including insertion sequence (IS) elements, contribute to genetic plasticity in ways that affect pathogenicity and virulence. The Principal Investigator hypothesizes that adaptive changes might include the evasion of immune defenses. At the molecular level, for example, gene expression could be affected by repeated or mobile genetic elements in several ways including transcriptional activation, insertional inactivation, transposition, deletion or gene amplification. The Principal Investigator further hypothesizes that as repeated sequence DNA including IS elements are likely important in gene regulation and genetic diversity in P. gingivalis, they will be found in association with virulence genes. Using P. gingivalis W83, the Principal Investigator has demonstrated the utility of a method initially described by Ohtsubo et al to isolate repeated DNA sequences carried by prokaryotic genomes. The Principal Investigator proposes to molecularly clone and characterize a diversity of repeated DNA sequences and use them as tools to evaluate positioning of such nucleotide sequences in P. gingivalis W83 with special reference to known virulence genes. The lysine gingipain protease (kgp) gene will be used as a paradigm virulence gene in the proposed studies. This information will be extended to non-clonal clinical isolates. In this fashion, the Principal investigator anticipates using this panel of repeated DNA sequences as tools in exploring the genetics of virulence in non-clonal P. gingivalis isolates. The gene probes that will emanate from the proposed studies will provide an operational link between the complete nucleotide sequence of strain W83 and the non-clonal pathogens commonly represented by typical isolates of P. gingivalis.